AudioServer: Add support for volume control

userspace/libraries/LibAudio/Audio.cpp

@@ -145,7 +145,7 @@ namespace LibAudio
 
 		LibAudio::Packet packet {
 			.type = LibAudio::Packet::Notify,
-			.parameter = 0,
+			.parameter = {},
 		};
 
 		send(m_server_fd, &packet, sizeof(packet), 0);

userspace/libraries/LibAudio/include/LibAudio/Protocol.h

@@ -40,6 +40,14 @@ namespace LibAudio
 			SetPin,         // parameter: pin number
 			                // response: nothing
 							// set the active pin of the current device
+
+			GetVolume,      // parameter: ignored
+			                // response: 10 * volume percentage (uint32_t)
+							// get the volume of the current device
+
+			SetVolume,      // parameter: 10 * volume percentage (uint32_t)
+			                // response: nothing
+							// set the volume of the current device
 		} type;
 
 		uint64_t parameter;